Method of forming composite metal bearings



METHOD OF FORMING COMPOSITE METAL BEARINGS Eric W. Weinman, Birmingham, Mich. assignor to General Motors Corporation, Detroit, Micln, a corporation of Delaware No Drawing. Filed Sept. 22, 1955, Ser. No. 536,022 7 Claims. c1. 29-196.3)

This invention relates to sintered powdered metal bearings and particularly to a method of securely bonding a sintered powdered copper base bearing part to a steel backing member.

Porous copper base bearings have been employed in industry during recent years, with the metal powder being conventionally sintered at relatively high temperatures.

In some instances the copper base powder is bonded to a steel back by the sintering operation. However, the copper base powder occasionally tends to shrink during the sintering operation and to pull away from the steel back. Inasmuch as a strong bond between the steel backingmember and the copper base powder is essential, it has been proposed heretofore to electrodeposit a suitable metal plate on the surface of the back to improve the strength of the bond. This type of process is disclosed in Koehring-Patents Nos. 2,187,086 and 2,198,253, owned by the assignee of the present invention. 7

Although the aforementioned procedure involving the use of an electrodeposited metal plate is suitable for many operations, occasionally the use of a single plate has proved to be inadequate. A principal object of the present invention, therefore, is to provide a novel method of securely sintering powdered copper base powders to a backing member formed of steel or other suitable ferrous metal. A further object of this invention is to provide a simple, inexpensive process for forming a sintered powdered copper base bearing by a procedure in which the copper base powder is caused to adhere strongly to a steel back.

, These and other objects are attained in accordance with my invention by the use of successively formed thinlayers of copper and tin on the backing member of the bearing. This process permits the elimination of the briquetting operation otherwise frequently employed. A suitable layer of loose copper powder is placed in contact with a steel strip, which has been preferably plated in the manner hereinafter described, and thereafter sintered at an appropriate elevated temperature.

In accordance with a preferred embodiment of the invention, the thin layer of copper is initially electrodeposited on the inner working surface of the steel strip or backing. A second thin layer of tin is thereafter provided, preferably by electrodeposition, on the surface of the copper layer. The combination of these two layers serves to improve the adherence of the copper base powder to the steel backing member. Following the sintering operation, the spongy copper base layer on the steel back is rolled to increase its density and subsequently re-sintered or annealed. The density of the sintered J powdered bearing layer can be further increased by additional rolling and annealing treatments.

sintered powdered copper base bearing layer can be Patented Apr. 4, 196.1

secured to a steel back. Hence the word bearing, as used herein, is intended to include all applications in which relatively moving parts are in engagement and in which high wear resistance and good antisco-re properties of the metal are desirable.

Composite sintered copper base bearings formed in accordance with the present invention can be provided with exceptional wear resistance as well as desirable oil-retaining properties. Moreover, such sintered powdered copper base bearings, when compared with similar parts made by normal manufacturing methods, do not require the extensive machining operations otherwise necessary to provide the proper tolerances. In turn, since little or no machining is necessary, scrap or waste is reduced to a minimum.

The wear resistance of the sintered powdered copper base bearing layer may be improved by the inclusion of an appropriate small amount of dispersed hard particles of various alloys. For example, copper base metal powders containing small amounts of titanium-aluminum, nickel-titanium and/or aluminum oxide powders possess outstanding wear resistance. These wear-resistant powdered copper base alloy bearing compositions are respectively disclosed in co-pending patent applications Serial Nos. 444,401, Thomson et. al.; 397,789, Thomson; and 478,484, Thomson, all of which are owned by the assignee of the present invention. If aluminum oxide is used, it is desirable to have the aluminum oxide present in the forlm of Alundurn or cornudum, either natural or artific1a Minor proportions of tin and/ or nickel powders are also preferably included in the powdered metal mix and serve to provide the material with greater corrosion resistance, ability to age harden, wear resistance and strength. The formed bearing part, when sintered, or when sintered and worked to a controlled degree of porosity, possesses excellent wear resistance properties due to the presence of the aforementioned type of dispersed hard particles.

The bearing is formed by initially thoroughly mixing the aforementioned types a powdered constituents, if they are to be included in the mix, with a suitable copper base powder. The nickel and/or tin may be alloyed with the copper, although normally they are separately added to the mix in powdered form. Other elements, such as zinc, nickel, lead, manganese, aluminum, silicon, beryllium, cobalt, iron and phosphorus, may also be included in the bearing material. Most of these elements normally may be wholly or partially alloyed with the copper. Zinc, nickel, lead and aluminum may be present in appreciable amounts and may be beneficial for particular purposes. Hence the zinc and lead contents of the copper base bearing may range as high as 45% and 30%, respectively. Likewise, up to approximately 15%. aluminum may be included in the powdered metal mixture, a 2% to 11% aluminum content being preferred for some applications. Nickel may be present in very large quantities, as hereinafter more fully explained. Silicon and iron, preferably in amounts of about 1% to 3% and 1% to 11%, respectively, may also be included. The various other elements listed above are normally present in only very small quanties.

The presence of even relatively minute amounts of the aforementioned types of hard particles improves the wear resistance of the bearing to a considerable extent, and the range of this type of constituent may vary from a small but effective amount to a quantity constituting approximately 15% by weight of the final mix. However, in order to provide the desired economy and strength, particularly impact strength and shock resistance, the hard particle content preferably should be maintained between about 0.25% and 7.5% by weight. For most appliczp tions it is preferred to use at least 1% of these particles to provide the bearing with outstanding wear resistance.

I have obtained best results when the copper constitutes between approximately 70% and 97% of the. total mix. However, it will be understood that the terms copper base metal, copper base bearing and copper base alloy, as used herein, are intended to encompass alloys and powdered metal mixtures in which copper is the major constituent and preferably constitutes at least 50% of such a powdered metal mixture or alloy.

Finely divided graphite, preferably 80 mesh or finer, may be mixed with the metal powder to improve frictional characteristics of the formed copper base bearing part. Small amounts of graphite not in excess of approximately 6.5% are satisfactory; while a graphite con- .tent between about 0.3% and 4% is normally preferred.

The inclusion of proper amounts of tin and nickel in the powdered metal mix further increases the wear re- .sistance and score resistance of the formed bearing part.

Moreover,-nickel also contributes corrosion resistance to the bearing and improves its ability to age harden. Tin melts at a low temperature and alloys with copper to form a tin-copper alloy, the latter coating the substantially pure copper particles. During the sintering operation, the elevated temperature causes the tin to diffuse through the copper. The melting point of the metal in the areas reviously occupied by the tin is thus raised, thereby providing an alloy having a melting point above the sintering temperature. Since the tin brazes the copper particles together to form a bronze, the resultant metal is a better bearing material than if no tin were present and possesses better corrosion resistance. Furthermore, the tin and nickel, if included in the powdered metal mix, serve to strengthen the bearing.

Although amounts of tin as high as 18% by weight may be used, optimum results are obtained with a preferred tin content between approximately 1% and 13%. The addition of tin in quantities greater than 18% results in the formation of hard and brittle copper-tin compounds, which tend to produce galling. Alternatively, a bronze powder of similar composition may be employed. The preferred nickel range is between 2% and although this element may be substituted for copper in amounts ranging from a small but effective amount up to the point where the copper content is only slightly higher than the nickel content. In no instance, therefore, would the added nickel content exceed about 49% in this copper base bearing material.

In view of the above considerations, I have obtained excellent results with a sintered powdered copper base bearing layer comprising approximately 0.3% to 4% by weight of carbon, tin not in excess of 13% by weight and the balance substantially all powdered copper. The inclusion of nickel in amounts not in excess of 15% by weight increases the corrosion resistance of the bearing and permits it to be more satisfactorily age hardened. As hereinbefore indicated, approximately 1% to 7.5% by weight of nickel-titanium alloy powder, titaniumaluminum alloy powder and/or crystalline aluminum oxide powder is preferably also included in the copper base mix to improve wear resistance of the resultant bearing.

The tin powder may be added in the form of tin dust, while the nickel may be introduced as nickel powder, such as electrolytic nickel powder or nickel produced from nickel carbonyl by means of the Mond process or other suitable means. Although nickel may also be used in other forms, it is desirable to add it in the form of nickel powder formed from nickel carbonyl as its commerically available fine particle size permits quicker homogenization. Electrolytic nickel powder, as cornmercially supplied, is somewhat coarser grained, and its use necessitates a longer period of time at an elevated temperature to sufficiently homogenize the powder metal mix.

Commercially pure copper and tin may be used or, as hereinbefore explained, a bronze powder of appropriate composition may be used in place of the mixture of copper and tin. Hydrogen reduced copper of approximately -15!) mesh has provided excellent results, although the particle size of the copper or bronze may vary from 60 to 325 mesh and still produce a satisfactory bearing. The particle sizes of other metal powders in the base material normally also should be within this range. However, if titanium-aluminum, nickel-titanium or aluminum oxide powders are used, mesh sizes between approximately 200 and -400 are conveniently and preferably employed. If these hard wear-resistant particles are too coarse, they are somewhat prone to cause scoring.

in accordance with the present invention, a bearing having a porous copper base layer of the above-described type can be produced without the necessity of a briquetting operation. Instead, a suitable layer of the loose copper base powder may be placed in contact with the reinforcing strip of steel which has been plated in the manner hereinafter described and thereafter sintered. Adherence of this powder to the steel is improved in accordance with this invention by the presence of the successively electroldeposited thin layers of copper and tin. It is preferred to initially electrodeposit a layer of copper having a thickness of approximately 0.0002 inch to 0.00045 inch on the steel or other ferrous metal back- .ing strip. Thereafter a layer of electrodeposited tin plate having a thickness ranging from approximately 0.00002 inch to 0.00015 inch is provided over the copper layer. For most applications, however, the minimum thickness of the tinlayer should be about 0.00008 inch.

Subsequently a mixture of the copper powder and pulverized tin, nickel, graphite and the aforementioned hard wear-resistant particles, if it is desired to add the latter constituents, are placed on the plated surface of the steel back.

This powder on the backing member is then sintered under suitable conditions of time, temperature and atmosphere into a structure having a controlled degree of porosity. Sintering temperatures between 1300 F. and 1950" F. and sintering times between fifteen and thirty minutes appear to be highly satisfactory. These sintering times are not critical, however, and sintering times as short as four minutes and as long as two hours produce satisfactory wear test results. Excellent results have been obtained by sintering the briquette at approximately 1650 F. for twenty minutes under a non-oxidizing furnace atmosphere, such as dissociated ammonia, dry Drycolene gas, or a gaseous mixture of Neutralene and a small amount of natural gas.

The dry Drycolene gas normally is composed of about 20% carbon monoxide, 3% hydrogen and 77% nitrogen. The Neutralene atmosphere mentioned above is a closely related gaseous mixture which usually consists of approximately 1.5% carbon monoxide, 1.5% hydrogen and 97% nitrogen. It has proved advantageous to use a mixture of 100 parts of Neutralene and one part of natural gas. Of course, other furnace atmospheres, such as hydrogen, mixtures of nitrogen and hydrogen or methane, etc., can be used, but Drycolene and Neutralene are readily available and each provides a highly effective protective atmosphere.

After the sintering operation the composite spongy copper base layer on the steel back is worked to increase its density, and this layer may thereafter be re-sintered or annealed. The density of the copper base layer can be further increased, if desired, by additional rolling and annealing treatments. For many applications it is preferable that the copper base bearing layer have a porosity between approximately 2% and 20%.

The presence of the electrodeposited tin layer increases the strength of the bond between the copper base powder and the steel back because this tin layer tends to promote wetting of the copper particles and increases the adherence of these particles to each other and to the base layer. During the sintering operation the tin layer will melt to a certain extent, along with any tin in the powdered copper base mix and cause the latter to become securely bonded to the tinned copper layer because of the wetting action of the tin. Further heating of the resultant composite bearing causes a thin bronze layer to be formed at the interface of the powdered copper and the back, and this bronze provides a very strong bond between these two components.

It should be noted that the use of either the electrodeposited copper layer or the tin layer alone will not provide the same results as the two-layer arrangement described above. In the case of a sintered powdered bronze bearing layer, copper plate alone is completely inadequate because it does notmelt at the sintering temperatures normally used. Likewise, although a tin layer which is applied directly to a steel backing will melt and bond the copper base bearing powder to the backing-it frequently forms brittle compounds with the iron at the sintering temperature. Hence the use of successively applied thin layers of copper and tin on a steel backing produces a composite bearing in which the powdered copper base metal, such as powdered bronze, is secured to the backing by a strong, non-brittle .bond.

The above-rescribed copper base bearing layer can be simultaneously produced on both the inside and outside surfaces of a steel backing sleeve to thereby form a bearing blank suitable for machininginto a floating bushing containing a steel core. This may be accomplished by positioning the sleeve in an annular chamber provided between two concentric cylinders or supporting sleeves. The space on either side of the bearing blank between this backing and the supporting cylinders then may be filled with the copper base powder. It is desired to use supporting sleeves formed of steel, preferably stainless steel. With the use of such supporting rings no briquetting or other application of pressure is necessary since these rings and the interjacent bearing components may be simultaneously vibrated to cause the copper base powder to settle into position.

Alternatively, a thin layer of the copper powder can be deposited on the electroplated copper and tin layers by a spraying operation. The copper base powder may be placed in a suitable container and thereafter blown or sucked through a gas flame so that it willcontact the tin layer in a molten or semi-molten state. An oxyacetylene flame is appropriate for this purpose. In this manner the powdered copper layer can be built up to any desired thickness, a thickness of 0.010 inch to 0.030 inch being typical. Thereafter the sprayer copper base powder layer is sintered in the manner described above.

With either of the procedures described above, briquetting is not required since proper densification can be obtained by rolling operations. When forming a composite bearing sleeve by the use of supporting rings, as described above, it is particularly desirable to increase the density of the copper base layer by a rolling operation since this powder is relatively loosely packed when placed in contact with the steel back. Of course, appropriate briquetting steps also can be employed if convenient.

If an appreciable amount of nickel has been separately included in the powder metal mix, heat treatment subsequent to sintering is beneficial. Thus a solution treatment for one to eight hours in a non-oxidizing atmosphere at a temperature between approximately 600 F.

and 1400 F. may be used to provide greater hardness and homogeneity. A two-step process is preferably employed, however, such as an initial heat treatment for five hours in a non-oxidizing atmosphere at 1400 F. followed by a water or oil quench and a low-temperature heat treatment or aging in a similar atmosphere for five hours at 600 F. The bearing may also be benefically aged at room temperature following the solution step.

6 While the present invention has been described by means of certain specific examples, it is to be understood that the scope of the invention is not to be limited thereby except as defined in the following claims.

I claim:

LA method of forming a composite bearing having a porous metal working surface, said method comprising electrodepositing a thin layer of copper on a surface of a steel backing strip, thereafter electrodepositing a thin layer of tin on said copper layer, placing a copper base powder into contact with said electrodeposited tin layer, and thereafter heating the coated backing strip and 'the contacting copper base powder to a temperature at which tin is molten to bond said powder by an essentially bronze layer to said backing strip.

2. A method of forming a composite metal bearing having a working surface of sintered copper base metal, said method comprising electrodepositing a layer of copper having a thickness of approximately 0.0002 inch to 0.00045 inch on a surface of a steel backing member, thereafter electrodepositing a layer of tin having a thickness between approximately 0.00002 inch and 0.00015 inch on said copper layer, placing a layer of copper base powder into contact with said tin layer, sintering said copper base powder for approximately four minutes to two hours at a temperature between about 1300 F. and 1950 F. under a non-oxidizing atmosphere whereby said copper particles are securely bonded by an essentially bronze layer to said backing member, and subsequently working the resultant sintered copper base layer to a desired degree of density.-

3. A process of forming a composite metal bearing having a working surface of sintered copper base metal, said process comprising electrodepositing a thin layer of copper on the surface of a steel backing, thereafter electrodepositing a thin layer of tin on said copper layer, spraying copper base powder through a gas flame into contact with said tin layer so that said powder contacts said tin layer before said powder has completely solidified, and subsequently heating said coated backing strip to sinter said powder and cause it to be bonded by an essentially bronze layer to said backing.

4. A method of forming a composite metal bearing having a working surface of sintered copper base metal, said method comprising electrodepositing a layer of copper having a thickness of 0.0002 inch to 0.00045 inch on a surface of a steel backing member, thereafter electrodepositing a layer of tin having a thickness of 0.00008 inch to 0.00015 inch on said copper layer, spraying copper base powder through an oxyacetylene flame into contact with said tin layer so that said powder melts while passing through said flame and contacts said tin layer before it has completely solidified, continuing said spraying step until a cooper layer having a thicknes between approximately 0.01 inch and 0.03 inch is formed on said tin layer, heating the formed copper base layer for approximately 15 to 30 minutes at at temperature of about 1300 F. to 1950 F. under a non-oxidizing atmosphere to further sinter said powder and cause the same to become securely bonded by an assentially bronze layer to said backing member, and thereafter rolling the resultant copper base layer to a desired degree of density.

5. A method of forming a composite meal bearing having a porous metal working surface, said method comprising electrodepositing a thin layer of copper on a surface of a steel backing strip, thereafter electrodepositing on said copper layer a tin layer which is substantially thinner than said copper layer, placing a copper base powder into contact with said electrodeposited tin layer, and thereafter heating the coated backing strip and the contacting copper base powder for a suflicient duration to concurrently interdiffuse said copper and tin layers, sinter said copper base powder and secure said copper base powder to said backing strip by an essentially bronze bond.

6. A method of forming a composite bearing having a porous metal working surface, said method comprising electrodepositing a layer of copper on a surface of a steel backing strip, thereafter electrodepositing on said copper layer a substantially thinner layer of tin, placing a copper base powder into contact with said elcctrodeposited tin layer, and thereafter heating the coated backing strip and the contacting copper base powder to a temperature below the temperature at which copper becomes molten but above the temperature at which tin becomes molten to concurrently interdiifuse said copper and tin layers,

sinter said powder and secure said powder to said backing strip by an essentially bronze bond.

7. A composite metal bearing comprising a steel supporting member, on said supporting member a comparatively thin, electrodeposited laminar copper-tin bonding layer which has been interdiifused to form a bronze layer and on said bronze layer an overlay of a copper base 8 powder joined to said backing strip by means of said bonding layer.

' References Cited in the file of this patent UNITED STATES PATENTS 2,092,018 Quarnstrom Sept. 7, 1937 2,187,086 Koehring Ian. 16, 1940 2,190,267 Light Feb. 13, 1940 2,198,253 Koehring Apr. 23, 1940 2,241,095 Marvin May 6, 1941 2,251,410 Koehring Aug. 5, 1941 2,266,330 Nachtman Dec. 16, 1941 2,299,877 Calkins Oct. 27, 1942 2,304,709 Rubin Dec. 8, 1942 2,428,318 Nachtman .2 Sept. 30, 1947 FOREIGN PATENTS 4 425,385 Great Britain Mar. 13, 1935 H- CERTIFICATE Patent No 2 977 673 April 4 1961 Eric W, Weinman It is hereby certified that error appears inthe above numbered patent requiring correction and that the said Letters Patent should read as corrected below Column 2 line .29 for ."cornudum" read ma corundum =--3 line 40 for "types a" read types of column 4 line 25 for electroldepoeited read w electrodeposited column 5 line 27 for 'above rescr'ibed read above described line 52 for sprayer read me sprayed column 6 line 54 for "cooper read copper same line for "'thicknes" read thickness line 63 for "meal" read me metal =9 Signed and sealed this 19th day of September 1961a SEA L) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No}, 2 ,977,,e7a April 4 1961 Erie W9 Weinman It is hereby certified that error efopears inthe above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column 2 line 29 for :"'eornudum"'- read eorundum 'line 4O for types a" read types of column 4 line 25 for electroldepo-eited readelectrodeposited column 5 line 27 A for 'above rescr'ibed read me above deecribed line 52 for sprayerread sprayed column 6 line 54 for "cooper" read copper same line for 'Lhicknes" read thickness line 63 for "meal read me metal =-=a Signed and sealed this 19th day of'Septem'ber 1961a (SEAL) Attest: o

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USC'OMM-DC 

7. A COMPOSITE METAL BEARING COMPRISING A STEEL SUPPORTING MEMBER, ON SAID SUPPORTING A MEMBER A COMPARATIVELY THIN, ELECTRODEPOSITED LAMINAR COPPER-TIN BONDING LAYER WHICH HAS BEEN INTERDIFFUSED TO FORM A BRONZE LAYER AND ON SAID BRONZE LAYER AN OVERLAY OF A COPPER BASE POWDER JOINED TO SAID BACKING STRIP BY MEANS OF SAID BONDING LAYER. 